(1) Field of the Invention
The invention relates to an organic electro-luminescence diode, especially to an organic light-emitting diode having serially stacked red, green, and blue light-generating units.
(2) Description of the Related Art
Two ways for conventional multicolor organic light-emitting diode (OLED) to generate three primary color light are that arranging red (R) green (G), and blue (B) light-generating units side by side, and combining a white light-generating unit with color filters. However, side by side patterns used in a manufacturing process of a flat panel will cause shadow effect. The shadow effect can be avoided by the other way such as combining the white light-generating unit with color filters, but the color filters may reduce the light intensity.
FIG. 1A shows a first type of conventional OLED panel with side by side patterns. R, G, and B light-generating units 20 are disposed side by side on a substrate 10. Each light-generating unit includes a hole injecting layer (HIL) 22, a hole transport layer (HTL) 23, an emission layer (EL) 24, an electron transport layer (ETL) 25 and an electron injecting layer (EIL) 26 sandwiched between two electrodes 21a and 21b. First of all, the electrode 21b used as an anode is formed on the substrate 10. Subsequently, the HIL 22, the HTL 23, the EL 24, the ETL 25 and the EIL 26 are formed on the electrode 21b in order. Finally, the electrode 21a is formed on the EIL 26 as a cathode. Referring to FIG. 1B, when different color ELs 24 are evaporated on the substrate 10, they are aligned for deposited on accuracy site by adjusting evaporating angle θ. The different evaporating angle θ causes ELs 24 evaporated non-uniformly in overall panel, and results in shadow effect.
FIG. 1C shows a second type of conventional OLED having a white light-generating unit with color filters. A red color filter layer 11, a green color filter layer 12 and a blue color filter layer 13 are formed on the substrate 10, and a white light-generating unit 20a is located on the three color filter layers 11, 12, and 13. As described in U.S. Pat. No. 6,696,177, the light-generating unit 20a can produce white light by a blue emission layer 201 containing an yellow fluorescence material. Because the light-generating units 20a in this type of OLED are not disposed side by side, the shadow effect does not occur. However, the luminance will be reduce due to the light going through the color filters 11, 12, and 13. Because different color lights have different luminance attenuation ratio, the luminescent efficiency of the blue light-generating unit and that of the red light-generating unit are usually lower than that of the green light.
In order to improve the disadvantages of forgoing two type of OLED, the inventor provides an OLED having serially stacked RGB light-generating units.